We’ve gotten this question a few times, and it’s a really good one. Since Rose’s Story takes place in the weeks before the beginning of Strung, it’s a fair assumption that it should be read first.
However, having read them all, I would advise you to read the trilogy first and then the prequel. It’s just so much better when you know Rose and have the full story first, I think.
Another option is to read Strung 1+2, then Rose’s Story, and then Strung 3. You could do it this way, but it might ruin the flow of the trilogy if you read the prequel in between.
It’s up to you 😊.
But if you want my opinion, read the trilogy first.